Using the peoxyxanthone reagent as one tool, data were obtained in previous collaborative work that validated the hypothesis that pharmacologic ascorbic acid is a pro-drug for preferential steady state formation of ascorbate radical and hydrogen peroxide in the extravascular space but not blood. Subsequent studies in the Molecular and Clinical Nutrition Section of NIDDK demonstrated that pharmacologic doses of ascorbate decrease growth of aggressive tumor xenografts in mice.[unreadable] [unreadable] Fluorinated molecules are excellent NMR probes. Work is in progress to develop fluorinated ascorbic acid analogues for NMR application that will be used in additional studies of the biological behavior of ascorbic acid.